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Grower’s Guide: What are Cold Frame Greenhouses?

Somewhere in your gardening research and tool browsing, you may have come across the term cold frame greenhouses. What are these structures and how can you utilize them to improve your planting efforts? We’ll explain more about these helpful and beneficial gardening solutions in this Grower’s Guide post.

What are Cold Frame Greenhouses?

Cold frame greenhouses are unheated structures that use solar energy and insulation to create a microclimate in your garden. Cold frames also provide a level of shelter and protection from wind and unpredictable external weather without overheating plants. With the added protection and slightly warmer environment, cold frames simply help prolong the growing season and ensure plant safety.

Unlike electric or gas heated greenhouses that use additional resources to set and maintain a specific climate, cold frames rely solely on the sun’s heat to create a slightly more balanced and warmer internal temperature. Many gardeners often utilize greenhouses as cold frames by simply not adding an extra heat source. But depending on size and material of your structure, not all cold frame designs accommodate an added heat source to create a greenhouse environment.

Cold frames come in multiple shapes and sizes, from small units with a hinged lid to high tunnel structures often used by commercial growers.

What Can You Use a Cold Frame Greenhouse for?

Cold frame greenhouses are most suitable to use during the few weeks before and after the last frost. Many regions experience frequently unpredictable weather when transitioning from winter to summer or summer to winter. With a cold frame, plant temperatures remain more stabilized in order to grow safely and efficiently in the spring and fall months. Here are a few ways to use a cold frame greenhouse:

Extend the season for cool-season crops. Because cold frames provide a slightly warmer and more controlled environment than external temperatures, these units help gardeners start plants without worry of frost or frozen ground. Plants won’t be affected by unseasonably cold or hot weather we often experience during spring and fall. Cold frames work great for cool-season plants as they can withstand the lower evening temperatures.

Harden off delicate plants and seedlings. Cold frame greenhouses help plants make the transition from indoor plants to outdoor plants. Whether you started seedlings in your home or a greenhouse, plants must gradually adjust to the change in temperature, sunlight, moisture, and exposure outdoors. With a cold frame, plants are controllably exposed to these changes, while still staying sufficiently protected. Once plants adjust to the climate change in your cold frame, then transplant them to your garden.

Tips for Growing in a Cold Frame Greenhouse

Cold frame greenhouses are relatively simple to use for any or all of the reasons listed above. However, keep these few tips in mind in order to maximize the benefits of your structure.

Choose the right location for your cold frame. In order to maximize warmth and sunlight and your cold frame, pick an optimal location to place your structure. Choose a south-facing spot that offers plenty of sunlight. Avoid spots near trees or other structures where snow or leaves can pile on your cold frame. This could result in damage to your structure or sunlight blockage.

Allow ventilation on hotter days. Too much warmth is not always a good thing – and that’s the benefit of a cold frame greenhouse. Since outdoor sunlight and temperature impact a cold frame’s internal temperature, easily adjust your cold frame during unseasonable heat waves. During these occasions, open your structure and allow sufficient airflow to give plants desired warmth without suffocating them.

Use your cold frame for growing within your means. As mentioned previously, cold frames are great for extending the growing season of cool-season vegetables in the spring and winter. When hardening off tender plants and seedlings, cold frames also allow for an easier transition for plants from inside to outdoors. Stick to options that survive within your location’s current climate range, not completely out-of-season plant varieties. The internal temperatures are only slightly warmer and more controlled than the outdoors. So, plants should handle the highs and the lows of your region fairly well while protected in your cold frame.

PRO TIP: Want to know what to grow in a cold frame or greenhouse year-round? Check out a few tips and tools for greenhouse growing in this blog post.